There are several types of prior art dispensing systems used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of printed circuit boards and integrated circuit chips. In this application, dispensing systems are used in the process of encapsulating integrated circuits with an encapsulating material and in the process of underfilling flip integrated circuit chips with an encapsulent. Prior art dispensing systems are also used for dispensing dots or balls of liquid epoxy or solder onto circuit boards and integrated circuits. The liquid epoxy and solder is used to connect components to a circuit board or to an integrated circuit. The dispensing systems described above include those manufactured and distributed by Speedline Technologies, Inc, the assignee of the present invention.
It is desirable to use positive displacement pumps in dispensing systems to effectively control the volume of material dispensed. U.S. Pat. Nos. 4,907,950 and 5,004,404 to Pierrat, which are incorporated herein by reference, disclose positive displacement pumps used to dispense variable quantities of material. The pumps disclosed by Pierrat include a crank-shaft drive that drives a number of pistons and cylinders to couple pressurized material at an inlet of the pump to an outlet of the pump to dispense the material. The pumps disclosed by Pierrat have up to four cylinders, each of which has an inlet port and an outlet port that are respectively coupled on a time-shared basis to the inlet and the outlet of the pump to provide dispensing.
Typical prior art pumps include a material distribution block to distribute material from the inlet of the pump to each of the inlet ports of the cylinders and from each of the outlet ports of the cylinders to the outlet of the pump. These distribution blocks are typically one piece blocks, constructed from a solid block of plastic or stainless steel, and have a number of passages drilled in the blocks to couple the inlet of the pump to each of the inlet ports and to couple each of the outlet ports to the outlet of the pump. For a pump having four cylinders, the distribution block typically has eight passages formed therein. The eight passages are coupled between 10 openings in the distribution block. Four of the openings are inlet port openings to couple to the inlet ports of the cylinders, four are outlet port openings to couple to the outlet ports of the cylinders, one of the openings is an inlet opening to couple to the inlet of the pump, and one of the openings is an outlet opening to couple to the outlet of the pump. Four of the eight passages are inlet passages that extend from one of the inlet port openings to the inlet opening, and the other four passages are outlet passages that extend from one of the outlet port openings to the outlet port.
While the distribution blocks are effective in distributing material between the cylinders and the inlet and the outlet on the pump, it is desirable to provide a distribution block that is less expensive to manufacture, and easier to clean. For some dispensing materials, such as those used in the assembly of printed circuit boards and integrated circuit chips, it is typically necessary to clean the dispensing material from a dispensing pump on a periodic basis to prevent dried material from clogging the pump.